<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <title>Title</title>
  </head>
  <body>
    <div id="app">{{username.toUpperCase()}} <br /></div>
  </body>
  <script src="./js/vue.js"></script>
  <script>
    const app = new Vue({
      //element 用来给Vue实例定义一个作用范围
      el: "#app",
      data: {
        username: "hello Vue",
      },
    });
  </script>
</html>
